thanks all.

This could happen due to many reasons:

1. Fine migration caused by LS water flooding as a result of altering the original rock wettability and blocking the pore spaces.

2. Clay swelling where many clay types, such as Montmorillonite, are more likely to swell and reduce the pore size when contacting LS water.

3. In tertiary recovery, heavier petroleum components are more likely to be present and these will require more advanced methods to be produced.